Astrocytic reaction predominance in chronic encephalitis of Junin virus-infected rats

Reactive astrogliosis in response to hemorrhagic fever virus: microarray profile of Junin virus-infected human astrocytes

BACKGROUND

Arenavirus Junin is the causative agent of Argentine hemorrhagic fever. Limited information is available concerning the pathogenesis of this human disease, especially the pathogenesis of acute and late neurological symptoms.

METHODS

In our study we present for the first time cDNA microarray profile of human astrocytes infected with the virulent strain of Junin virus. Transcriptional profiling was confirmed by quantitative real-time RT-PCR and cytokine/chemokine/growth factor assay.

RESULTS

We demonstrated the impact of virus infection on immune/inflammatory response/interferon signaling and apoptosis. Pro-apoptotic response and amplification with time of pro-inflammatory cascade of human astrocytes suggested neurodegenerative dysfunctional reactive astrogliosis in response to Junin virus infection.

CONCLUSION

Our results suggest potential pathogenic role of astroglial cells in the development of neurological symptoms and late neurological syndrome during Argentine hemorrhagic fever.

Junín virus. A XXI century update

Junín virus of the Arenaviridae family is the etiological agent of Argentine hemorrhagic fever, a febrile syndrome causing hematological and neurological symptoms. We review historical perspectives of current knowledge on the disease, and update information related to the virion and its potential pathogenic mechanisms.

Mice lacking alpha/beta and gamma interferon receptors are susceptible to junin virus infection

Junin virus (JUNV) causes a highly lethal human disease, Argentine hemorrhagic fever. Previous work has demonstrated the requirement for human transferrin receptor 1 for virus entry, and the absence of the receptor was proposed to be a major cause for the resistance of laboratory mice to JUNV infection. In this study, we present for the first time in vivo evidence that the disruption of interferon signaling is sufficient to generate a disease-susceptible mouse model for JUNV infection. After peripheral inoculation with virulent JUNV, adult mice lacking alpha/beta and gamma interferon receptors developed disseminated infection and severe disease.

Astrocyte response to Junín virus infection

In a previous study of experimental murine encephalitis induced by Junín virus (JV), an arenavirus, we showed increased expression of iNOS by unidentified cells, concomitant with the astrocyte reaction. The specific inhibition of iNOS was associated with greater mortality but lower astrocytosis, suggesting that the protective role of nitric oxide (NO) synthesized by iNOS was related to enhanced astrocyte activation, representing a beneficial cellular response to virus-induced central nervous system damage. In the present work, cultured astrocytes were used to study whether JV infection could trigger iNOS expression and assess its eventual relationship with viral replication, glial fibrilary acidic protein (GFAP) expression levels and the presence of apoptosis. We found that JV infection of astrocytes did not induce apoptosis but produced both increased iNOS synthesis, detected by immunocytochemistry and fluorescence activated cell sorting (FACS) analysis, and increased NO, which was indirectly measured by nitrite/nitrate levels. These changes occurred early relative to the increases in GFAP expression, as detected by immunocytochemistry, FACS analysis and RT-PCR. The fact that iNOS inhibition abolished enhanced GFAP expression in infected monolayers suggests that NO was directly involved. In addition, iNOS inhibition enhanced virus replication. Together with data from confocal microscopy, these results suggest that JV induces iNOS expression in infected astrocytes and that the resulting NO has an important role both in reducing viral replication and in enhancing subsequent astrocyte activation.

Junin virus-induced astrocytosis is impaired by iNOS inhibition

Because Junin virus (JV) experimental encephalitis of mice and rats is characterized by mild histopathological changes that do not seem to justify per se lethality after intracerebral infection, such a murine model seems adequate to investigate the potential role of inducible nitric oxide synthase (iNOS) as a pathogenic factor. Concomitant with a predominant astrocyte reaction, increased immunoperoxidase expression of iNOS, mitochondrial superoxide dismutase (SODm) and glutathione peroxidase (GPX) was disclosed in brain of mice infected with JV strain #44. When specific inhibition of iNOS was achieved by intraperitoneal administration of amino guanidine (AG), significantly greater mortality was observed in treated animals (70% vs. 40%), together with similar infective titers ( approximately 10(7) PFU/g) but lower astrocytosis, as shown by glial fibrillary acidic (GFAP) labeling. As regards SODm and GPX immunochemical expression in neurons, no differences were found between mice with or without AG treatment. The present results suggest that the apparent protective role of nitric oxide (NO), when synthesized by iNOS, is unrelated to reduced viral replication but rather to enhanced astrocyte activation behaving as a beneficial cell response to virus-induced CNS damage.

Glial fibrillary acidic protein (GFAP) immunochemical profile after junin virus infection of rat cultured astrocytes

Cultured astrocytes derived from newborn rat brain were inoculated with Junin virus (JV) to characterize their response to infection by means of their glial fibrillary acidic protein (GFAP) immunochemical profile. Samples from 1 to 11 days post-inoculation (pi), as well as matched controls, were serially harvested for GFAP labeling by peroxidase-antiperoxidase (PAP) method. It was only at day 3 that significantly greater values of GFAP staining (P < 0.05) were disclosed by three complementary approaches: image analysis, ELISA and immunoblot densitometry. Since such increase was abolished by Triton X-100 treatment, soluble GFAP fraction appeared responsible for the early though transient enhancement of GFAP immunoreactivity that followed viral inoculation.

Immunoperoxidase tracing of Junin virus neural route after footpad inoculation

To determine the pathway adopted by peripherally inoculated Junin virus (JV) to reach the CNS, rat tissues were serially harvested to trace the sequence of viral progression from right hind footpad to brain. Immunoperoxidase (PAP) labeling of viral antigen, concomitantly with infectivity assays and histological examination of each selected sample, were carried out. As from the 2nd week post-infection (pi), neurological disease inducing 100% mortality at 1 month was evident. At day 5 pi, viral antigen was first detected at footpad level in epidermic and dermic cells, as well as in neighbouring myocytes; labeled macrophages infiltrating small nerve branches were also disclosed. As from 10-15 days pi, viral antigen became apparent along ipsilateral sciatic nerve structures and within lumbar spinal ganglion neurons, followed by a fast viral spread throughout CNS neurons that involved spinal cord and brain. Concurrent histopathology featured minimal inflammatory reaction together with generalized astrocytic activation. Hematogenous viral transport was negligible, since JV was isolated much earlier and in higher infectivity titers in neural tissues than in blood. It may be concluded that after viral replication in footpad, JV neural route was demonstrated by its PAP labeling from peripheral nerves to cerebral cortex.